UN: 'Convincing evidence' of Syria chemical attack

This photo released by the United Nations shows professor Ake Sellstrom, head of the chemical weapons team working in Syria, handing over the report on the Al-Ghouta massacre to Secretary-General Ban Ki-moon Sunday Sept. 15, 2013. (AP Photo/United Nations, Paulo Filgueiras)
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This photo released by the United Nations shows professor Ake Sellstrom, head of the chemical weapons team working in Syria, handing over the report on the Al-Ghouta massacre to Secretary-General Ban Ki-moon Sunday Sept. 15, 2013. (AP Photo/United Nations, Paulo Filgueiras)
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French President Francois Hollande, left, welcomes U.S. Secretary of State John Kerry for a meeting on Syria at the Elysee Palace in Paris, Monday, Sept. 16, 2013. (AP Photo/Michel Euler)
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French President Francois Hollande, left, gestures as he talks to U.S. Secretary of State John Kerry, upon his arrival at the Elysee Palace in Paris, Monday, Sept. 16, 2013. (AP Photo/Michel Euler)— AP

French President Francois Hollande, left, gestures as he talks to U.S. Secretary of State John Kerry, upon his arrival at the Elysee Palace in Paris, Monday, Sept. 16, 2013. (AP Photo/Michel Euler)
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U.S. Secretary of State John Kerry, right, and British Foreign Secretary William Hague, left, listen to French Foreign Minister Laurent Fabius speak at a news conference after a meeting on Syria, at the Quai d'Orsay, Paris, Monday, Sept. 16, 2013. (AP Photo/Larry Downing, Pool)— AP

U.S. Secretary of State John Kerry, right, and British Foreign Secretary William Hague, left, listen to French Foreign Minister Laurent Fabius speak at a news conference after a meeting on Syria, at the Quai d'Orsay, Paris, Monday, Sept. 16, 2013. (AP Photo/Larry Downing, Pool)
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From left, British Foreign Secretary William Hague, French President Francois Hollande, U.S. Secretary of State John Kerry and French Foreign Minister Laurent Fabius pose upon their arrival at the Elysse Palace in Paris, prior to a meeting on Syria, Monday, Sept. 16, 2013. (AP Photo/Michel Euler)— AP

From left, British Foreign Secretary William Hague, French President Francois Hollande, U.S. Secretary of State John Kerry and French Foreign Minister Laurent Fabius pose upon their arrival at the Elysse Palace in Paris, prior to a meeting on Syria, Monday, Sept. 16, 2013. (AP Photo/Michel Euler)
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French Foreign Minister Laurent Fabius, left, U.S. Secretary of State John Kerry, right, and British Foreign Secretary William Hague, second right, pose for the media prior to a meeting on Syria at the Quai d'Orsay in Paris, Monday, Sept. 16, 2013. (AP Photo/Francois Mori, Pool)— AP

French Foreign Minister Laurent Fabius, left, U.S. Secretary of State John Kerry, right, and British Foreign Secretary William Hague, second right, pose for the media prior to a meeting on Syria at the Quai d'Orsay in Paris, Monday, Sept. 16, 2013. (AP Photo/Francois Mori, Pool)
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U.S. Secretary of State John Kerry waves a goodbye to Saudi foreign minister Prince Saud Al-Faisal Bin Abdul Aziz, unseen, in his car, right, following their working lunch in a Paris restaurant, Monday Sept. 16, 2013. The U.S. and its closest allies laid out a two-pronged approach in Syria on Monday, calling for enforceable U.N. benchmarks for eradicating the country's chemical weapons program and an international conference bolstering the moderate opposition. (AP Photo/Remy de la Mauviniere)— AP

U.S. Secretary of State John Kerry waves a goodbye to Saudi foreign minister Prince Saud Al-Faisal Bin Abdul Aziz, unseen, in his car, right, following their working lunch in a Paris restaurant, Monday Sept. 16, 2013. The U.S. and its closest allies laid out a two-pronged approach in Syria on Monday, calling for enforceable U.N. benchmarks for eradicating the country's chemical weapons program and an international conference bolstering the moderate opposition. (AP Photo/Remy de la Mauviniere)
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U.S. Secretary of State John Kerry, right, and French Foreign Minister Laurent Fabius arrive for a news conference at the Quai d'Orsay after a foreign ministers meeting to discuss developments in Syria, Paris, Monday, Sept. 16, 2013. The U.S. and its closest allies laid out a two-pronged approach in Syria on Monday, calling for enforceable U.N. benchmarks for eradicating the country's chemical weapons program and an international conference bolstering the moderate opposition. (AP Photo/Larry Dow— AP

U.S. Secretary of State John Kerry, right, and French Foreign Minister Laurent Fabius arrive for a news conference at the Quai d'Orsay after a foreign ministers meeting to discuss developments in Syria, Paris, Monday, Sept. 16, 2013. The U.S. and its closest allies laid out a two-pronged approach in Syria on Monday, calling for enforceable U.N. benchmarks for eradicating the country's chemical weapons program and an international conference bolstering the moderate opposition. (AP Photo/Larry Dow
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CORRECTS CAPTION - Chair of the Commission of Inquiry on Syria Brazilian Paulo Pinheiro informs the media during a press conference after presenting the Commission's report to the 24th session of the Human Rights Council at the European headquarters of the United Nations in Geneva, Switzerland, Monday, Sept. 16, 2013. (AP Photo/Keystone, Salvatore Di Nolfi)— AP

CORRECTS CAPTION - Chair of the Commission of Inquiry on Syria Brazilian Paulo Pinheiro informs the media during a press conference after presenting the Commission's report to the 24th session of the Human Rights Council at the European headquarters of the United Nations in Geneva, Switzerland, Monday, Sept. 16, 2013. (AP Photo/Keystone, Salvatore Di Nolfi)
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From left, French Foreign Minister Laurent Fabius, U.S. Secretary of State John Kerry, French President Francois Hollande and British Foreign Secretary William Hague, pose in the lobby of the Elysee Palace in Paris, prior to a meeting on Syria, Monday, Sept. 16, 2013. (AP Photo/Philippe Wojazer, Pool)— AP

From left, French Foreign Minister Laurent Fabius, U.S. Secretary of State John Kerry, French President Francois Hollande and British Foreign Secretary William Hague, pose in the lobby of the Elysee Palace in Paris, prior to a meeting on Syria, Monday, Sept. 16, 2013. (AP Photo/Philippe Wojazer, Pool)
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UNITED NATIONS 
U.N. inspectors said Monday there is "clear and convincing evidence" that chemical weapons were used on a relatively large scale in an attack last month in Syria that killed hundreds of people.

The findings represent the first official confirmation by scientific experts that chemical weapons were used in Syria's civil war, but the report left the key question of who launched the attack unanswered.

The rebels and their U.S. and Western supporters have said the regime of President Bashar Assad was behind the Aug. 21 attack, while the Syrian government and its closest ally, Russia, blame the rebels.

U.S., British and French diplomats said the findings of the U.N. inspectors supported their conclusion that Assad regime was to blame. Russia disagreed.

Secretary of State John Kerry briefed U.S. allies on a broad agreement reached over the weekend with Russia to end Syria's chemical weapons program, pressing for broad support for the plan that averted U.S. military strikes. Kerry met in Paris with his counterparts from France, Britain, Turkey and Saudi Arabia before seeking a U.N. resolution that would detail how the international community can secure and destroy Syria's stockpile and precursor chemicals.

And in Geneva, the chairman of a U.N. war crimes panel said it is investigating 14 suspected chemical attacks in Syria, dramatically escalating the stakes. Paulo Sergio Pinheiro said the panel had not pinpointed the chemical used or who is responsible.

Secretary-General Ban Ki-moon presented the U.N. inspectors' report to a closed meeting of the U.N. Security Council before its release.

"This is a war crime and a grave violation of ... international law," Ban told the council in remarks distributed to the press. "The results are overwhelming and indisputable. The facts speak for themselves. ... The international community has a responsibility to hold the perpetrators accountable and to ensure that chemical weapons never re-emerge as an instrument of warfare."

The inspectors' report said "the environmental, chemical and medical samples we have collected provide clear and convincing evidence that surface-to-surface rockets containing the nerve agent sarin were used ... in the Ghouta area of Damascus" on Aug. 21.

"The conclusion is that chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic, also against civilians, including children, on a relatively large scale," the inspectors said in their report to Ban.

"This result leaves us with the deepest concern," they added.

Syria initially called for a U.N. investigation of an alleged chemical attack on Khan Al-Assal near Aleppo on March 19, which it blamed on the rebels. But when the U.S., Britain and France reported other alleged attacks, the secretary-general insisted on broadening the investigation, which the Syrians opposed.

After months of negotiations, an agreement was reached in August for U.N. inspectors to go to the sites of Khan Al-Assal and two other alleged attacks. But its mandate was limited, reportedly at Syria's insistence, to report on whether chemical weapons were used and if so which ones - not on who was responsible.